Existing event message communication systems, such as building fire and security systems typically send event information or premise data in the form of analog data tones that are formatted as digital data to central monitoring centers. Such event messages are sent via the Public Switched Telephone Network (PSTN) or cellular (telephone) networks. The digital data included in the message can be sent in several different ways. Typically, the data is sent using a Dual Tone Multiple Frequency (DTMF) or Frequency Shift Key (FSK) signaling, but other techniques can be used. Specific examples of DTMF and FSK communication protocols are Ademco® Contact ID Protocol (“SIA DC—05”) and the “SIA Format” Protocol (“SIA DC—03”).
Time-based communication protocols usually define specific timing requirements and tolerances for receiving event messages. Today's receiving equipment manufacturers typically extend the timing tolerance of the communication protocol beyond the defined limits in order to allow signals from premises that do not meet the published standard limits or to account for equipment variations over time. This is common practice in the industry.